Membrane desiccation heat pump

ABSTRACT

There is provided a system for pumping thermal energy. The system includes (a) a heater for heating a liquid, (b) a gas-liquid contactor for adding vapor from the liquid to a process gas to produce a vapor-containing gas, and (c) a membrane permeator for removing the vapor from the vapor-containing gas and for providing a resultant vapor. The system transfers a quantity of thermal energy from the heater to the resultant vapor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is claiming priority of U.S. Provisional PatentApplication Ser. No. 60/251,207, which was filed on Dec. 4, 2000, andU.S. Provisional Patent Application Ser. No. 60/257,031, which was filedon Dec. 21, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a transfer of thermal energy,and more particularly, to heat transfer arrangements employing amembrane desiccation heat pump for both heating and coolingapplications.

2. Description of the Prior Art

A cooling of a gaseous fluid containing humidity and, in particular, acooling of humid air, is desired in many circumstances. Cooling ofambient atmosphere is often desired in buildings, domestic dwellings, inappliances such as refrigerators, and in storage rooms and the like. Itis also desired in delivery vehicles and trucks, and in aircraft andmarine craft. Other applications are natural gas cooling for removal ofnatural gas liquids or providing of controlled inert atmosphere toindustrial processes such as paint drying, food drying and clean rooms.

Cooling systems using water vapor as working fluid are among the oldestin the art of producing cold. Early processes made use of principles ofboth compression and adsorption refrigeration, the latter using sulfuricacid as an absorbent. Vacuum refrigeration systems using water vapor ororganic vapor as a refrigerant and steam injector as a compressor werewell adapted to air conditioning application in the 1940s.

Many different proposals have been made for cooling gases and, inparticular, for the cooling of air. A popular system in widespread useutilizes a compression and expansion of a heat exchange medium in theform of a gas, which can be compressed into a liquid state, and then isallowed to expand into a vapor state, i.e., the so-calledcompression/expansion cycle. In most cases, chloro-fluoro carbon gases,e.g., Freon™, were used, but recently such gases have been consideredenvironmentally unsafe. Conventional alternatives to Freon™ are not asefficient as Freon™, and thus systems using the compression-expansioncycle require a relatively large input of power for the compressioncycle. As a result, attention has turned to the feasibility of airconditioners that rely on alternative energy sources. Desiccant airconditioning systems are able to utilize alternative sources such aswaste heat or solar energy for cooling and air conditioning therebyreducing electric power consumption and reducing reliance uponconventional power sources.

Desiccant air conditioners work as follows. During a cooling mode oradsorption cycle, hot humid air enters an intake side of an airconditioning system and passes through one side of a slowly turningdesiccant wheel or circular desiccant bed. Water vapor and othermoisture vapor are adsorbed on an extended desiccant material surfacearea, drying the air and releasing latent heat of condensation. Hot dryair from the desiccant bed wheel then passes through a heat exchangersuch as an air-to-air heat exchanger wheel giving up some of the heat toan exhaust air stream. The air is then reconditioned to be in a desiredcomfort zone by passing through an evaporative element or unit wheremoisture is evaporated back into the air, for example by spraying,cooling the air to a desired temperature and humidifying the air to adesired relative humidity.

Open cycle desiccant systems have been known from the early 1940's. In1955, U.S. Pat. No. 2,700,537 to Pennington described using rotary heatexchangers impregnated with desiccants. Today dual path machines stilluse the Pennington cycle. In 1960, U.S. Pat. No. 2,926,502 to Muntersimproved this cycle. The '502 patent discloses an air conditioningsystem including the recycling of air, at least three air flow paths,with all embodiments including a recycling of interior space conditionedair path, an open cycle regeneration path and a supplementary air pathfor an additional heat exchanger.

U.S. Pat. No. 4,594,860 to Coellner et al. discloses an open cycledesiccant air conditioning system in which the regeneration path is anopen cycle and very similar to Pennington's cycle. U.S. Pat. No.2,186,844 to Smith discloses a refrigeration apparatus wherein heat froma mechanical refrigeration unit regenerates desiccant, very similar toconcepts described in U.S. Pat. No. 5,502,975 to Brickley et al. andU.S. Pat. No. 5,517,828 to Calton et al. The common factor is the opencycle regeneration path. U.S. Pat. No. 4,786,301 describes an airconditioning system having heat exchanging desiccant bed withalternating adsorption/desorption cycles, an improvement of this conceptis described in U.S. Pat. No. 5,222,375 entailing the use of twoalternating desiccant beds.

U.S. Pat. No. 5,353,606 to Yoho et al. addresses a three-path desiccantair conditioning system. As with other prior art systems, all theseregeneration paths are open cycle.

Some of the problems associated with desiccant air conditioners are theneed for removal of latent heat of condensation and adsorption from thedesiccant bed and desiccant material during the adsorption cycle, theneed for thermal energy for the desiccant regeneration cycle and theneed to cool the desiccant after the regeneration. Furthermore,desiccant wheel machines are cumbersome to build and require a highlevel of maintenance.

Several authors have suggested employing a heat pump to raise thetemperature of heated fluid for utilization of a waste heat stream. Heatpump systems employed for such processes are based on conventionalcycles, i.e., fluid compression, absorption, sorption and desiccationcycles. The use of heat pumps for heat recovery have been shown inseveral applications utilizing various low level heat sources such asheat emitted by refrigerators (U.S. Pat. Nos. 4,041,724 and 4,226,089),an exhausted air duct (U.S. Pat. Nos. 4,100,763, 4,175,403 and4,416,121), paper mill processes (U.S. Pat. Nos. 4,026,035, 4,437,316,4,522,035 and 4,780,967), a power plant (U.S. Pat. No. 4,124,177), solarenergy (U.S. Pat. Nos. 4,143,815, 4,332,139 and 4,703,629). Othersources of low level heat are: a plurality of secondary heat sourcesfrom an industrial plant or a factory (U.S. Pat. Nos. 4,173,125,4,307,577, 4,333,515 and 5,548,958.); humid air (U.S. Pat. Nos.4,197,713 and 4,517,810); air exhausted from a paint spray booth (U.S.Pat. No. 4,197,714); a gas stream of a drying oven (U.S. Pat. No.4,295,282); a building stack or a flue (U.S. Pat. Nos. 4,314,601 and4,660,511); waste heat from a gas turbine (U.S. Pat. No. 4,347,711);thermally activated separation processes such as fractionaldistillation, distillation, dehydration, or acid gas scrubbing (U.S.Pat. Nos. 4,347,711 and 5,600,968); waste water heat (U.S. Pat. No.4,448,347); fumes from a heating boiler (U.S. Pat. No. 4,523,438);boiling solvent vapor (U.S. Pat. Nos. 4,537,660 and 4,539,816); wasteheat heated water (U.S. Pat. No. 4,819,446); waste heat such as absorberheat, hot vapor heat, flue gases, or a combination thereof (U.S. Pat.No. 5,255,528).

A membrane separation method for removing water vapor from a gas is amethod wherein a gas containing water vapor is contacted to one side ofa vapor permselective membrane assembly, and a dry gas is contacted tothe other side of the membrane, so that the water vapor is selectivelypermeated and separated through the membrane. In principle, it hasmerits over other three methods such that the running cost is low, thestructure of the apparatus is simple, and dry air can continuously beobtained without polluting air. As a vapor permselective membraneexcellent in permeability of water vapor, an ion exchange membrane aswell as a dehumidifying method using such a membrane has been proposedby U.S. Pat. Nos. 3,735,558 and 4,909,810. Hollow fiber membrane-baseddehydration is also known. See, for example, U.S. Pat. Nos. 4,783,201,4,725,359, 4,718,921, 4,497,640, 4,583,996 and 3,511,031. U.S. Pat. No.4,900,626 discloses a hollow composite fiber for dehydration having apolydimethylsiloxane coating on a dense layer of the fiber support.

Although membranes have been used in various separation applications,their use for heat pump systems has been limited. U.S. Pat. Nos.4,152,901 and 5,873,260 propose to improve an absorption heat pump byusing a semi-permeable membrane and a pervaporation membrane,respectively. U.S. Pat. No. 4,467,621 proposes to improve vacuumrefrigeration by using a sintered metal porous membrane and U.S. Pat.No. 5,946,931 shows a cooling evaporative apparatus using a microporousPTFE membrane.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a membranedesiccation heat pump system that is useful for various application suchas cooling, chilling, heating and air conditioning, and that islow-cost, efficient and simple to maintain.

Another object of the present invention is to provide such a membranedesiccation heat pump system, characterized by an energy economy orefficiency better than that of prior art systems. One important featureof the present invention is that it employs a process carried outwithout an addition of costly heat energy from outside for separating asorption agent from a working medium.

Another object of the present invention is to provide a membranedesiccation air conditioning system, which permits a greater degree ofindependent control of temperature and humidity for achieving parameterlevels in desired regions of the comfort zone than prior art systems.

A further object of the present invention is to provide an open systemmembrane desiccation air conditioner having a broad range ofapplications and being capable of net introduction of either heat ormechanical energy from an external source and net removal of heat energyrelative to the air conditioning system for greater flexibility andcontrol of comfort zone parameters.

Additional objects of the present invention are to provide a membranedesiccation based liquid chilling and heating process systems usable forvarious applications.

Yet another object of the present invention is to provide a new methodof waste or low level energy recovery using a membrane desiccation-basedheat pump process adapted to extract unusable thermal energy from amedia at low temperature and upgrade it to a higher, useful temperature.

A first embodiment of the present invention is a system for pumpingthermal energy. The system includes (a) a membrane permeator forremoving vapor from a process gas and for providing a vapor-depletedprocess gas, and (b) a gas-liquid contactor for adding vapor from aliquid to a the vapor-depleted gas to produce a vapor-added process gas.The system transfers a quantity of thermal energy from the liquid to thevapor-added process gas.

A second embodiment of the present invention is a system for pumpingthermal energy including (a) an energy source for heating avapor-containing gas, and (b) a membrane permeator for removing vaporfrom the vapor-containing gas and for providing a resultant vapor. Thesystem transfers a quantity of thermal energy from the energy source tothe resultant vapor.

A third embodiment of the present invention is a system for pumpingthermal energy including (a) a heater for heating a liquid, (b) agas-liquid contactor for adding vapor from the liquid to a process gasto produce a vapor-containing gas, and (c) a membrane permeator forremoving the vapor from the vapor-containing gas and for providing aresultant vapor. The system transfers a quantity of thermal energy fromthe heater to the resultant vapor.

The present invention also contemplates methods for employing thesystems described herein.

A first method for pumping a quantity of thermal energy includes thesteps of (a) adding vapor from a liquid to a process gas, thus yieldinga vapor-containing gas, and (b) employing a membrane permeator to removethe vapor from the vapor-containing gas, thus providing a resultantvapor. The quantity of thermal energy is transferred from the liquid tothe resultant vapor.

A second method for pumping a quantity of thermal energy includes thesteps of (a) employing a heater to heat a vapor-containing gas, and (b)employing a membrane permeator to remove vapor from the vapor-containinggas, thus providing a resultant vapor. The quantity of thermal energy istransferred from the heater to the resultant vapor.

A third method for pumping a quantity of thermal energy includes thesteps of (a) employing a heater to heat a liquid, (b) adding vapor fromthe liquid to a process gas to produce a vapor-containing gas, and (c)employing a membrane permeator to remove the vapor from thevapor-containing gas, thus providing a resultant vapor. The quantity ofthermal energy is transferred from the heater to the resultant vapor.

A fourth method for pumping thermal energy includes the steps of (a)removing vapor from a process gas with a membrane permeator to yield avapor-depleted gas, and adding vapor from a liquid to a thevapor-depleted gas via a gas-liquid contactor to yield a vapor-addedgas. The method transfers a quantity of thermal energy from the liquidto the vapor-added gas.

The present invention involves a membrane desiccation heat pump for usein association with a gaseous flow system adapted to move a gaseousprocess fluid, such as air, containing a quantity of moisture vaporcontent. In a preferred embodiment, the cooling system includes (a)humidification means, e.g., a gas-liquid contactor, operable to addvapor of a vaporizable liquid fluid to a process gaseous fluid, (b) amoisture vapor membrane permeator, (c) means for passing the processfluid through the membrane permeator to dry the process fluid andsubstantially reduce the quantity of moisture vapor in the processfluid, thereby separating the vapor from the gaseous process fluid and(d) vapor removal means for removing the concentrated vapor from thefrom the membrane permeator. An evaporation process utilizes heat fromone of the fluids or from both for the latent heat of vaporization ofthe liquid, to reduce the temperature thereof and simultaneouslyestablish a desirable humidity level in such gaseous process fluid.

One feature and advantage of the present invention is that the membranedesiccation heat pump permits a substantial import of energy from anexternal source, such as an alternative or low level energy source, intothe system, and a substantial removal of heat energy from the system.Thus, the present invention provides a very efficient heat pump both forthe purpose of either cooling or heating.

The liquid-gas contactor facilitates mass transfer of liquid vapor froma liquid into a gas while simultaneously removing latent heat from theliquid and thereby reducing the temperature of both. It also acts as adirect-contact heat exchanger that enables a heat transfer from a fluidthat has to be cooled to a circulating fluid. It may be any unit thatoperates on a principle common in the industry such as spray oratomizing, dripping, sprinkler, wet pad, packed column, plates column,baffle tower or any type of cooling tower. It could also be a membranecontactor having any of the configurations described above for themembrane permeator assembly, however, in this case, it would enable theevaporation from the liquid to the gas phase. Other possible embodimentsfor such a contactor include a humidifier or any type of evaporator, forexample, a short tube evaporator or a long tube evaporator, or a flashevaporator.

A membrane separator removes vapor from a stream of carrier gas. Theremoval of the vapor from the gas stream is also involves a removal ofthe latent heat contained in the vapor, thus providing a thermodynamicvehicle for a heat pump.

For use in the present invention, a membrane separator assembly ispreferably capable of an efficient and economical separation of vaporfrom the carrier gas. Such a membrane separator assembly may come indifferent shapes and forms. The following paragraphs describe severalfeatures of the membrane assembly that may be used for vapor separationin the present invention:

The membrane separator assembly may include one or more membrane unitsthat could be assembled in any array, such as series, parallel, cascadeor in a membrane column. A membrane unit may be either a self-containedmodule or a combination of one or more membrane elements in a housing. Amembrane element can be any form of packaging of membrane area in asingle item such as but not limited to a module, a cartridge, a plate,etc.

The membrane can be solid or liquid, organic or inorganic, pre-made ordynamic, charged or uncharged, ionic or non-ionic, hydrophilic orhydrophobic, porous or dense, permeable, non-permeable or semipermeable. It can be polymeric, metallic, ceramic, carbon or glass.Membrane geometry can be in any form such as a flat sheet, tubular,capillaries, hollow fibers or a monolith. A membrane element can be inany configuration such as hollow fiber module, hollow fiber plates,spiral wound module, plate and frame, pleated or folded cartridge,envelopes, bags, tubes and sheets, spiral tubes, candles or monolithic.

Flow patterns of either a feed-retentate side or a permeate side of themembrane in the membrane unit may be countercurrent, co-current or both.It could be transverse flow, diagonal flow or random direction flow. Itcould be unidirectional or multi directional. It could be one pass ormulti pass. Either flow could be on any side of the membrane in theelement configurations detailed above.

Removal of the permeating vapor from the membrane unit may be direct orit could be facilitated by means such as reflux flow, either internal orexternal, vacuum and/or condensation. It could be a sweep stream thatmay be of gas or liquid. Such a sweep stream may be inert or reactive,i.e., having either physical or chemical affinity toward the permeatingvapor.

A good membrane process for vapor separation from gas especiallydehydration must be capable of removing water vapor from the feed gas tothe desired dew point. Preferably, the water vapor separation takesplace with as little loss of feed gas to the permeate as possible andthe process must economically perform this separation; in other words,the membrane surface area required to perform a given water vaporseparation should be as small as possible.

Vapor permeates through a membrane from a feed side of the membrane to apermeate side of the membrane. A driving force for a transport of vaporthrough the membrane is a partial pressure differential of the vaporacross the membrane. Therefore, a partial pressure of water vapor in agas leaving as permeate from a membrane module cannot exceed a partialpressure of water vapor in a feed gas entering the membrane module. Inmost cases, the partial pressure of water in a gas at saturation is verylow. Therefore, the partial pressure driving force for the vaportransport must be provided by one of three methods: (1) a sweep method,in which dry gas from an external source is swept proximate to thepermeate side of the membrane; (2) a vacuum method, in which a vacuum isapplied to the permeate side of the membrane; or (3) a dilution method,in which (a) the permeate is left at, for example, atmospheric pressure,but either a small percentage of the feed gas is allowed to permeate themembrane, diluting the water vapor content of the permeate, or (b)reflux of a part of the dry retentate into the permeate compartment. Inall three cases, the driving force for the permeation of the vapor inthe feed gas is provided by the vapor partial pressure differencebetween the feed and the permeate.

The membrane desiccation heat pump can be constructed in severalconfigurations. It may be either an open cycle or closed cycle gassystem, and it may be either an open cycle or closed cycle liquidsystem. The system may be operated either in a cooling mode or in aheating mode. It may also determine both the temperature and the vaporcontent of the out put gas. Specifically, the membrane desiccation heatpump may serve as a very efficient air condition system both for largeand small sizes, and it may be an excellent system for providingchilling water for various applications.

As in any heat pump, the laws of thermodynamics govern the membranedesiccation heat pump. It removes heat from a media at a low temperatureand transfers it to a higher temperature by investing external energyinto the process. Commonly, a compression heat pump requires mechanicalenergy input, and an absorption heat pump requires thermal energy inputto facilitate the thermodynamic process. A membrane desiccation heatpump can utilize either form of energy input or both together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of a membrane desiccation heat pumpsystem in accordance with the present invention.

FIGS. 2A-2C are conceptual diagrams of several possible flow modes ofpermeate in a membrane permeator.

FIGS. 3A-3C are conceptual diagrams of several possible arrangements forremoval of permeate from a membrane permeator.

FIG. 4 is a conceptual diagram of a totally open cycle gas chillingsystem.

FIG. 5 is a conceptual diagram of an open cycle gas chilling/airconditioning system.

FIG. 6 is a conceptual diagram of a liquid chilling—open cycle system.

FIG. 7 is a conceptual diagram of a gas chilling—closed cycle system.

FIG. 8 is a conceptual diagram of a closed cycle liquid chilling system.

FIG. 9 is a conceptual diagram of gas chilling/air conditioning andvapor content control system.

FIG. 10 is a conceptual diagram of an open cycle liquid chilling systemwith a permeate vacuum pump.

FIG. 11 is a conceptual diagram of a liquid chilling system with apermeate reflux dilution.

FIG. 12 is a conceptual diagram of a gas chilling/air conditioning andvapor content control system.

FIG. 13 is a conceptual diagram of a membrane heat pump in a heatingmode.

FIG. 14 is a conceptual diagram of a membrane heat pump in a heatingmode with a liquid side heater.

FIG. 15 is a conceptual diagram of a membrane heat pump used forrecovery of heat from a cooling tower.

FIG. 16 is a detailed conceptual diagram of an open cycle membrane heatpump used for recovery of heat from a cooling tower.

FIG. 17 is a graph of heat pump coefficient of performance as functionof heat rejection temperature.

FIG. 18 is a graph of heat pump coefficient of performance as functionof heat source temperature.

FIG. 19 is a psychometric chart of a thermodynamic cycle of a membraneair conditioning system.

FIG. 20 is a psychometric chart of a thermodynamic cycle of a membraneheat pump.

FIG. 21 is a psychometric chart of a thermodynamic cycle of a membraneheat pump for recovering heat from a cooling tower.

FIG. 22 is a psychometric chart of a thermodynamic open cycle of amembrane heat pump for recovering heat from a cooling tower.

DESCRIPTION OF THE INVENTION

Before proceeding with a description of the present invention, it iswell to define certain terms as used herein.

A heat pump is a system that utilizes a thermodynamic process that takesthermal energy from a low temperature heat source and releases it athigher temperature utilizing an input of energy from another source.

A membrane is a semi permeable barrier capable of selectively permeatingcertain constituents of a fluid mixture.

A membrane permeator is a self-contained assembly of membrane packaging,including all required housings and piping components, capable ofrendering perm selective separation of a fluid mixture.

Desiccation is a process for removing vapor of one or more liquids outof a gas containing the vapor, resulting in vapor-depleted or dry gas.Usually this is done by an adsorption material such as a zeolite or asilica gel. However, it can be done by absorption for example,absorption of water vapor by sulfuric acid.

A fluid is a substance with no reference configuration of permanentsignificance, aggregate of matter in which molecules are able to flowpast each other without fracture planes forming. Subdivisions of fluidsare gases vapors and liquids.

A gaseous fluid is a fluid where its volume is a function of itspressure and its absolute temperature. All gaseous fluids approximatelyobey the ideal gas equation pv=nRT where p is pressure, v is volume, nis number of moles, R is the gas constant (0.082 liter atm/deg K) and Tis absolute temperature.

FIGS. 1-16 are schematic drawings illustrating various exemplaryembodiments of the present invention. Auxiliary equipment, such aspumps, valves, heat exchangers and condensers, is not necessarily shown.

FIG. 1 is a conceptual diagram of a membrane desiccation heat pumpsystem 100 in accordance with the present invention. System 100 uses, asoperating media, a gas in a gas loop 105 and a condensable fluid in aliquid loop 110. System 100 obtains thermal energy from a warm liquid 7,which is at a first temperature, transfers the energy to avapor-containing gas 1 and then outputs the energy as a concentratedvapor 125 at a second, higher temperature. The terms “cold, cool, warmand hot”, as used herein, are meant to indicate relative temperatures ofvarious media, and not necessarily absolute temperatures of the media.

Vapor-containing gas 1 enters a feed side of a membrane permeator 2 thatcontains a permselective membrane 3 for selective permeation of vaporfrom vapor-containing gas 1. The permeation of vapor fromvapor-containing gas 1 removes the vapor and energy fromvapor-containing gas 1. The energy is output in the form of latent heatcontained by concentrated vapor 125, which exits membrane permeator 2from a permeate side thereof via a permeate exit 4.

Warm dry gas 5 leaves membrane permeator 2 via a retentate side thereof,enters gas-liquid contactor 6 and interacts with, e.g., directlycontacts, warm liquid 7, which also enters gas-liquid contactor 6. As aresult of the interaction between the two fluids, i.e., warm dry gas 5and warm liquid 7, evaporation occurs. Flow modes of the fluids ingas-liquid contactor 6 may be counter-current as shown in FIG. 1, orthey may be co-current or cross current. Energy for the latent heat ofthe evaporation is taken from warm liquid 7, resulting in a decrease inthe temperature of both fluids, i.e., warm dry gas 5 and warm liquid.Thus, a cold liquid 8 and a cold gas, i.e., vapor-containing gas 1, exitgas-liquid contactor 6 and are respectively recirculated.

A liquid circulation loop may include a liquid reservoir 9 and acirculation pump 10. A gas recirculation loop may include a pumpingmeans 11, such as a blower or a compressor. Optionally, a heat exchanger19 may be installed to increase the efficiency of the process bytransferring thermal energy between warm dry gas 5 and cold liquid 8, byindirect contact therebetween, and more specifically, by precooling warmdry gas 5 before it enters gas-liquid contactor 6.

FIGS. 2A-2C show permeate flow within several alternate embodiments ofmembrane permeators suitable for use as membrane permeator 2.

FIG. 2A shows a membrane permeator 202A having a mixed permeate flowconfiguration. Permeate passes through a permselective layer of apermselective membrane 203A and then exits via a permeate exit 204A. Allof a gas required to dilute a permeate stream comes from a feed gas. Inmixed-flow, the gas, i.e., vapor and gas to be dried, on the permeateside of a given section of the membrane blends with the other gas thatpermeates other sections of the membrane in such a way that permeationthrough that section may be calculated according to the average permeateconcentration. Such permeate flow typically occurs in spiral woundmembrane module, transversal hollow fiber module and some plate andframe module.

FIG. 2B shows a membrane permeator 202B in which permeate flows in aco-current configuration. A permeate concentration is ever increasing asit flows down a permeate channel parallel to a feed side flow, through apermselective membrane 203B, and exits via a permeate exit 204B at adown stream end of membrane permeator 202B.

FIG. 2C shows a membrane permeator 202C in which permeate flows in acounter current configuration, which is usually more favorable than thatof either the mixed or co-current configurations. As a more dilutepermeate from a down streamside of membrane permeator 202C flows in acounter direction to a feed side flow, it cumulatively blends withpermeate from preceding sections to lower their concentration andthereby increase a driving force across a permselective membrane 203Cresulting in a higher permeate flux. The dilute permeate exits viapermeate exit 204C, which is located at an upstream side of membranepermeator 202C.

FIGS. 3A-3C illustrate several means to facilitate higher permeate flowin a membrane permeator by lowering a vapor concentration on a permeateside of the membrane permeator.

FIG. 3A shows permeate removal by vacuum. This may be done either by avacuum pumping means 13, which may be, for example, a vacuum pump or asteam injector. A condenser 12, from which a condensate 15 exits, islocated between membrane permeator 2 and vacuum pumping means 13. Thisconfiguration with condenser 12 substantially reduces pump capacityrequirements of vacuum pumping means 13, as vacuum pumping means 13 isused only to remove non-condensable gas. Energy consumption of vacuumpumping means 13 should be taken into account for calculating heat pumpefficiency. Generically, condenser 12 is an embodiment of a heatexchanger.

FIG. 3B shows an arrangement for removal of permeate by counter currentreflux. A reflux stream 14 of dried gas is drawn from downstream of aretentate outlet of membrane permeator 2 and directed into a permeatechannel of membrane permeator 2. An energy investment here is in a formof compression energy invested in reflux stream 14. Condenser 12 is usedwhen the gas has to be recovered or when the condensation is to be used.

FIG. 3C shows an arrangement for dilution of a permeate stream by meansof sweeping, using a sweep stream 18 that may be either a liquid or agas. Optionally, a separator 16, which may be a condenser, from which astream of condensate 15 and a stream of a liquid-depleted sweeper 17would exit, if the sweep fluid were a gas. If sweep stream 18 is aliquid of other chemical composition than the vapor from membranepermeator 2, separator 16 may be any appropriate equipment capable ofseparating the condensate of the vapor from membrane permeator 2 fromthe liquid sweep stream 18, such as by extraction crystallization ordistillation.

An overall effect of operation of a heat pump system such as that shownin FIG. 1 is to reduce the temperatures of the circulating fluids.However, as will be disclosed in greater detail below, the combinedemployment of membrane desiccation and evaporation in the mannerindicated herein yields a more efficient heat pump than the desiccantheat pumps described in the prior art, which include adsorptiondesiccation using adsorbent materials such as zeolites.

Vapor desiccation by either solid or liquid desiccants is an exothermicprocess that requires substantial means for removing thermal energyemitted during the adsorption process owing to the operation costrequired for removing the emitted energy, the investment in equipmentdedicated for this purpose and the complexity of such systems.Furthermore, the desiccants have to be regenerated. Such regenerationtypically requires either a pulsating operation or a use of adesiccation wheel, which is cumbersome to construct, operate andmaintain.

In addition to having a more efficient separation of vapor from gas,compared to desiccant based processes, the system of FIG. 1 offers anumber of other advantages over prior art systems, including a heat pumphaving a higher efficiency with lower equipment cost, a reducedlikelihood of maintenance problems with the lower operation cost, acapability for use with simple equipment due to the lack of need foradsorbent regeneration. The same is true if the heat pump process iscompared to either absorption or compression expansion refrigerationcycles; there is no need for expensive pressure-piping and fittings,compressors and other component that render such systems expensiveespecially when large volume of fluids are involved. Compared to suchsystems membrane heat pump would operate at relatively low pressures andwill not need special fluids such as Freon™, Halon™ or ammonia. Thepresent invention may employ inexpensive and environmentally friendlyand safe to use fluids such as air and water and still operate veryefficiently.

FIG. 4 illustrates a system similar to that of FIG. 1 with the exceptionthat both fluids operate in open cycle modes. A warm humid gas stream,i.e., vapor-containing gas 1, enters membrane permeator 2. A dry warmgas, i.e., warm dry gas 5, and warm liquid 7 enter gas-liquid contactor6, where both warm dry gas 5 and warm liquid 7 consume part of their owncombined enthalpy to provide latent heat for liquid evaporation and willexit the system at lower temperatures. The two exit streams are a coldgas 20, which contains liquid vapor, and cold liquid 8.

FIG. 5 illustrates another embodiment of the present invention. Thesystem in FIG. 5 is a gas chilling system that differs from the systemin FIG. 1 in that the gas stream operates in an open cycle while liquidcirculates in a closed cycle. Warm humid gas, i.e., vapor-containing-gas1, is pumped from liquid reservoir 9 using circulation pump 10 andenters membrane permeator 2. Warm dry gas 5, and warm liquid 7, which iscirculating, enter gas-liquid contactor 6. Cold gas 20 exits the system,while cold liquid 8 flows via heat exchanger 19 and back into liquidreservoir 9. Cold gas 20 may be pumped into an enclosed space 24 that,in a case of an air conditioning process, may be a building. When thesystem of FIG. 5 is employed for air conditioning, the gas fluid (i.e.,vapor-containing gas 1, dry gas, 5 and cold gas 20) is air and theliquid fluid (i.e., warm liquid 7 and cold liquid 8) is water.

The system of FIG. 5 may be utilized for applications in any industrialinstitutional or residential field where chilled gas is required. One ofthe most common applications is air-conditioning, which will bediscussed further below. Other applications include industrial gasprocessing or natural gas treatment maintenance of a cool inert gasenvironment such as that employed in food, produce and pharmaceuticalindustries.

FIG. 6 illustrates a heat pump system similar to that of FIG. 1 with theexception that the liquid operates in an open cycle mode, and the gasloop circulates in a closed cycle. A gas stream is circulated in aclosed loop by pumping means 11. Vapor-containing gas 1 enters membranepermeator 2. Warm dry gas 5 and warm liquid 7 enter gas-liquid contactor6. Cold gas 20 exits gas-liquid contactor 6 and is recycled asvapor-containing gas 1 into membrane contactor 2, via heat exchanger 19,thus pre-cooling incoming warm liquid 7. Cold liquid 8 flows out of thesystem.

The system of FIG. 6 may be utilized for applications in any industrialinstitutional or residential field where chilled water is required. Forexample, the system may be employed to provide chilled water for foodprocessing and dairy, chilling cooling water for plastic fabricationmachinery, chilling condenser-cooling water, and cold water for buildingcooling systems.

FIG. 7 illustrates an embodiment of the present invention similar tothat of FIG. 1, but differs from FIG. 1 in that an additional heatexchanger 21 is installed on the gas closed-loop. A heat transfer-fluidenters heat exchanger 21 as a warm or hot fluid 22, exits heat exchanger21 as a chilled fluid 23 and circulates to an end-user.

FIG. 8 illustrates a system similar to that of FIG. 7, but differs byhaving heat exchanger 21 installed on the liquid circulating closedloop. Both embodiments shown in FIGS. 7 and 8 advantageously can be usedwith a suitable pair of liquid/gas fluids and can be operated at optimalconditions in enclosed modes without a need for direct contact of theprocess fluids with an end-user. Also, having an enclosed conditionavoids fouling of the system components by constituents of the fluid,which may otherwise occur in an open cycle system.

FIG. 9 illustrates an open cycle gas cooling system with an ability tocontrol vapor content of an outlet gas. This embodiment is similar tothat of FIG. 5, but differs in that cold gas 20, which exits gas-liquidcontactor 6 with a high level of humidity, enters a second membranepermeator 25 where the humidity is reduced to a desired level bypermeating the vapor through the a membrane 26. A dry cold gas 27 exitsthe system and may be delivered to an end-user.

Using a dual permeator system as that shown in FIG. 9 enables a higherthermodynamic efficiency since the overall load of moisture circulatingin and out of enclosed space 24 is substantially lower than thatachieved in FIG. 5; therefore, reducing the separation requirement ofpermeator 2. Such employment of a membrane desiccation heat pump is verysuitable for air conditioning as it provides both an efficient coolingof air and an ability to maintain moisture at a comfort level. For airconditioning, air, i.e., dry cold gas 27, is delivered to a building,i.e., enclosed space 24, and the feed air, i.e., vapor-containing gas 1,is drawn from an inner space of the building.

FIGS. 10 and 11 show two embodiments of a liquid chilling system thatare embellishments of the embodiment shown in FIG. 6. The systems ofFIGS. 10 and 11 receive warm liquid 7 and provide cold liquid 8 to aconsumer.

Dry gas 5 exits from a retentate outlet of membrane permeator 2 andpasses through a cooling heat exchanger 29, which may be either aircooled or water cooled, and enters gas-liquid contactor 6 whereevaporative cooling occurs. Cold gas 20 and warm liquid 7 are eachrouted through heat exchanger 19, and produce a precooled liquid streaminto gas-liquid contactor 6.

Optionally, the systems in FIGS. 10 and 11 may include a heater 28 thatreceives a gas stream from heat exchanger 19. Heater 28 may use heatfrom a low level heat source, waste heat or any other convenient heatsource. There are three reason for this heating. The first reason is toelevate the temperature of the gas stream from heat exchanger 19 toincrease the thermodynamic efficiency of the heat pump. The secondreason is to increase the permeability of permselective membrane 3,which is temperature dependent. The third reason is to enable membranepermeator 2 to operate at a high vapor pressure. Operating at a highvapor pressure increases the driving force of vapor through thepermselective membrane 3, elevates the dew point of the permeating vaporand thereby reduces the energy required for permeate removal means,i.e., higher level of vacuum or less reflux.

Another energy input is via pumping means 11, e.g., a blower, whichincreases pressure and temperature of vapor-containing gas 1 because ofgas compression. Pumping means 11 thus elevates the pressure at the feedside of the membrane permeator 2 and improves the membrane separation,which is very dependent on a ratio between feed and permeate pressures.

Options for permeate removal are shown vacuum pumping means 13 in FIG.10 and as reflux stream 14 in FIG. 11. Either the power of vacuum pumpmeans 13 or the pressure energy loss of reflux stream 14 is included inthe energy consumption of the heat pump. One should realize that thereis no need for all of these energy inputs and each one of them alonewould render an efficient system. The systems in FIGS. 10 and 11 may beconstructed with heater 28 or may rely only on pumping means 11 as itssource of energy. However, having heater 28 will also preventcondensation of vapor in the gas loop due to the gas compression.Optional cooling heat exchanger 29 may pre cool gas 5 before enteringcontactor 6. These systems may vent part of, or the entire volume of,gas used for the membrane separation via a vent 31. They may alsorecycle part of, or the entire volume of, gas used for this purpose viaa port 30 back into the gas loop. A gas make-up port 32 enablescompensation for gas lost in the membrane separation.

FIG. 12 illustrates a system in which low level waste heat is used forair conditioning. Generally, the membrane desiccation heat pump of thepresent invention can utilize any source of thermal or mechanical energyto render an efficient operation. The system in FIG. 12 is an extensionof the embodiment of FIG. 9.

In FIG. 12, heater 28 uses waste heat to heat vapor-containing gas 1from a building, i.e., enclosed space 24. Gas make-up port 32 is usedfor supplying the system with fresh air. Both membrane permeators 2 and25 use reflux streams 14 to efficiate vapor permeation, and both ventwater vapor permeate streams through their respective permeate exits 4to the atmosphere via vents 31. A retentate stream, i.e., warn dry gas5, coming out of the membrane permeator 2 is brought back to ambienttemperature by cooling heat exchanger 29 using cooling water, and isthen precooled by heat exchanger 19 before it enters gas-liquidcontactor 6.

FIG. 13 illustrates an embodiment of a membrane desiccation heat pumpoperating in a heating mode. Generally, this heat pump will take inlow-level heat that can be provided at low-temperature. Exemplarysources of low-level heat include waste heat, solar heat, geothermalheat or heat from a low-temperature heat sink.

In FIG. 13, the low-level heat is taken in the form of a stream 34 thatcontains waste heat at temperature T2. Heat in an amount of Q2 is takeninto the closed liquid cycle from stream 34 using a heat exchanger 33.This heat is conveyed to the gas stream as the latent heat of the liquidvapor through gas-liquid contactor 6. The humid gas stream receives anadditional amount of heat Q1 at heater 28 that operates at temperatureT1 and heats vapor-containing gas 20. The vapor is separated from thegas at membrane permeator 2 and releases its latent heat throughcondenser 12 at temperature T0, which is substantially higher than T2.Heat Q0 is released at condenser 12, where released thermal energyQ0=(Q1+Q2), such that temperature T0 is delivered to an end-user by aheat conveying fluid stream 35.

In FIG. 13, as well as in any of the embodiment of the presentinvention, gas-liquid contactor 6 may be an evaporator of any kind, forexample, a cooling tower, a packed column, a distillation column or anyother type of unit operation equipment used for such purpose. Heater 28may be of any type and may utilize steam, hot water, fuel or gasburning, electrical, geothermal or solar, or any other heat source thatraises the temperature of the gas vapor stream to a desired temperature.As shown in FIG. 13, liquid condensate 15 from condenser 12 may bepumped into liquid reservoir 9 and reflux stream 14 may be pumped backinto the gas loop. Any of the configurations given in FIGS. 2 and 3 maybe used for membrane permeator 2.

Referring again to FIG. 12, note that the system of FIG. 12 may alsooperate in a heating mode. To enable the heating mode, no cooling waterpasses through cooling heat exchanger 29 and the permeate streams frompermeate exits 4 are routed to condensers from which condensate flowsback to liquid reservoir 9, in a manner similar to that shown in FIG.13.

Any of the membrane heat pumps of the present invention may be employedin a heating mode or a cooling mode. For example, to configure thesystem shown in FIG. 13 for a cooling mode, chilled fluid will bedelivered to the end-user from heat exchanger 33 via a fluid stream 36.Condenser 12 is cooled by ambient temperature cooling water. Waste-heatmay be used for heater 28. Thus, in this mode the heat pump takes energyQ2 from stream 34, adds to it waste energy Q1 at heater 28, and emits tothe environment energy Q0=Q1+Q2.

FIG. 14 shows another embodiment of a membrane heat pump in a heatingmode. FIG. 14 differs from FIG. 13 by having heater 28 installed on theliquid loop. The waste heat may be delivered to the system via either ofheat exchanger 33 or heat exchanger 29, or via both heat exchanger 33and heat exchanger 29.

FIG. 15 shows an embodiment of a membrane desiccation heat pump used forrecovering of waste heat from a cooling tower. This embodiment differsfrom the embodiment of FIG. 13 by having a cooling tower 135 in the rolegas-liquid contactor 6. Cooling tower 135 may of any type but ispreferably an induced air or forced air type. Waste heat Q2 is deliveredto the system via warm water, i.e., warm liquid 7 at temperature T2. Ifwaste heat Q2 from warm liquid 7 is not captured, then energy containedtherein is lost as cooling tower 135 releases vapor to the openatmosphere. The amount of energy that is released to the environmentfrom cooling towers is huge, but it is not ordinarily useful becausetemperature T2 is relatively low and cannot be used for mostapplications. However, in FIG. 15, cooling tower 135 cools warm liquid 7and transfers waste heat Q2 to the air stream through the latent heat ofthe water vapor.

In FIG. 15, the vapor saturated air that comes out of cooling tower 135is heated in heater 28, which utilizes a heat source that provides atemperature T1 and inserts the heat amount Q1 into the air vapormixture. The vapor is permeated at membrane permeator 2, exits membranepermeator 2 as a concentrated vapor stream, and enters condenser 12where useful heat Q0=Q1+Q2 is released at a desired high temperature T0and is delivered to an end-user by heat conveying fluid stream 35. Sucha process may be operated as a closed cycle as shown in FIG. 15 or as anopen cycle as shown in FIG. 16.

The thermodynamic a thermally driven heat pump may be presented by theequationQ 2 /Q 1 =T2(T2−T0)/T1(T0−T2)where T represents absolute temperature and subscripts 1, 2 and 0 referto the heat source, the absorbed heat and the rejected heat,respectively. The Ratio Q2/Q1, which indicates the refrigeration effectper unit of energy input, is known as Coefficient of Performance or COP.

FIGS. 17 and 18 are graphs that show a calculated Coefficient ofPerformance of a membrane heat pump as a function of a heat sourceabsolute temperature T₁, an absorbed heat temperature T₂, and a rejectedheat temperature T₀, where the efficiency is given as a ratio Q₁/Q₂,where Q₁ is a driving heat invested in the process, Q₂ is the absorbedheat, and the sum Q₁+Q₂ equals the rejected heat.

FIG. 19 is a psychometric chart of a thermodynamic cycle of a membraneair conditioning system, e.g., FIG. 5. Point “a” corresponds to theentry of the membrane permeator. The air undergoes membrane desiccationalong pass a-c and its humidity is reduced from Ha to Hc. Pass c-d ispre-cooling in the heat exchanger at constant humidity Hc. Pass d-b isadiabatic evaporative cooling in the gas-liquid contactor at constantenthalpy hb. From point b the air goes back to the end-user. Pass b-erepresents the additional desiccation by a second membrane contactor,e.g., FIG. 9. Humidity is reduced and the enthalpy of the air is alsoreduced, resulting in greater comfort.

FIG. 20 is a psychometric chart of a thermodynamic cycle of a membraneheat pump as shown in FIG. 13. Point “a” corresponds to the entry of themembrane permeator. The air undergoes membrane desiccation along passa-c and its humidity is reduced from Ha to Hc. Enthalpy is reduced fromha to hc. An amount of heat Q0=ha-hc is carried through the membrane inthe form of latent heat and is released to an end-user via condenser 12.Pass c-b is an evaporation in the gas-liquid contactor while theenthalpy increases from hc to hb. In this pass the waste heat that iscontained in the liquid is conveyed to the gas in the form of vaporlatent heat. Pass b-a is heating in heater 28 at constant moisturecontent Hb. It raises the temperature of the vapor gas mixture totemperature ta. Then the gas flows back into the membrane contactor viapumping means 11.

The following calculation example demonstrates the process:

Along pass c-b (FIG. 20), air goes into gas-liquid contactor 6 at:

-   Tc=158° F. (70° C. or T0=343° K),-   Hc=0.022 lb water/lb air, and

Hc=66 btu/lb air enthalpy Temperature Enthalpy Moisture content Point t°F., t° C., T° K. h (btu/lb) H (lb water/lb air) a 158, 70, 343 96 0.050Heater's Exit≅ permeator's Entry c 158, 70, 343 66 0.022 permeator'sExit≅ contactor's Entry b 104, 40, 313 83 0.050 contactor's Exit≅Heater's EntryData were taken from Perry's Chemical Engineer's Handbook, sixthedition, McGraw-Hill Book Company 1984, pp. 12-5.

The heating energy Q1=ha−hb=96−83=13 btu/lb air. The energy released inthe form of water vapor enthalpy through the membrane isQ2=hb−hc=83−66=17 btu/lb air.

Calculating the Coefficient of Performance: COP=Q2/Q1=17/13=1.31.Knowing that Q2/Q1=T2(T2−T0)/T1(T0−T2), assuming no thermal losses andsolving for T1, one obtains T1=392° K or 119° C. or 246.2° F.

If a steam heater is to be used it would require steam of 27.9 psia toachieve this performance. Data were taken from Perry's ChemicalEngineer's Handbook, sixth edition, McGraw-Hill Book Company 1984, pp.3-237.

Assuming a membrane heat pump that requires to produce heat Q0=100,000btu/hour. If Q2/Q1=X and Q0=Q1+Q2 then Q1=Q0/(1+X), and X=1.31 ascalculated above. Thus a steam heater will needQ1=100,000/(1+1.31)=43,290 btu/hr.

Since the heat of condensation of the steam used (27.9 psia) is 935btu/lb, the steam flow rate required is 43,290/935=46.3 lb steam perhour. The total enthalpy released from the air at membrane permeator 2is Q0=17+13=30 btu/lb air. Therefore the amount of air circulating is100,000/Q0=100,000/30=3,333 lb air/hr.

The amount of vapor that passes into the air at gas liquid contactor 6is equal to the change in the moisture content of the airHa−Hc=0.050−0.022=0.028 lb water/lb air, resulting in 0.028*3,333=93.3lb water/hr.

The average latent heat of water vapor at between 104° F. and 159° F. is1,030 btu/lb water. Thus, the amount of energy required to evaporatethis water is 93.3*1,030=96,133 btu/hr. Assuming a waste heat comes inas a stream of water at 45° C. (113° F.) and leaves at 40° C. (104° F.)and water heat capacity of 1 btu/lb ° F, then the water flow rate willbe 96,133/(113−104)=10,681 lb/hr or 80.9 liter per minute.

FIG. 21 is a psychometric chart of a thermodynamic cycle of a membraneheat pump for recovering heat from a cooling tower, as shown in FIG. 15.FIG. 22 is a psychometric chart of a thermodynamic open cycle of amembrane heat pump for recovering heat from a cooling tower, as shown inFIG. 16. In both FIGS. 21 and 22, one may see that latent heat energy ofthe vapor is upgraded by having its temperature increased using heater28 and then released to the end-user by means of membrane permeator 2.In a conventional system, if one would like to recover energy that istransferred to air steam 20 from warm water stream 7 processed incooling tower 135, and subsequently upgraded by heater 28, without firstseparation of vapor from air stream 1, it could not be done efficientlydue to size of the heat exchanger required. One of the great advantagesof the present invention is that by carrying our such separation usingmembrane permeator 2 the need to handle the entire air stream iseliminated since only the permeate stream has to be processed to recoverthe latent heat. Therefore the size of condenser 12 is more than oneorder of magnitude smaller than such heat exchanger.

It should be understood that various alternatives and modifications ofthe present invention could be devised by those skilled in the art. Thepresent invention is intended to embrace all such alternatives,modifications and variances that fall within the scope of the appendedclaims.

1-36. (canceled)
 37. A system for pumping thermal energy, comprising: aheater for heating a liquid; a gas-liquid contactor for adding vaporfrom said liquid to a process gas to produce a vapor-containing gas; anda membrane permeator for removing said vapor from said vapor-containinggas and for providing a resultant vapor; wherein said system transfers aquantity of thermal energy from said heater to said resultant vapor. 38.The system of claim 37, further comprising a heat exchanger throughwhich said resultant vapor is routed for heating a media.
 39. The systemof claim 38, wherein said resultant vapor heats said media bycondensation and releases latent heat.
 40. The system of claim 37,wherein said vapor permeates from a feed side of said membrane permeatorto a permeate side of said membrane permeator, and wherein said systemfurther comprises an arrangement for increasing a driving force betweensaid feed side and said permeate side.
 41. The system of claim 40,wherein said arrangement employs a technique selected from the groupconsisting of (a) sweeping a dry gas proximate to said permeate side,(b) applying a vacuum to said permeate side, and (c) allowing a portionof said vapor-containing gas to permeate said membrane.
 42. The systemof claim 37, wherein said membrane permeator discharges a retentate gas,and wherein said arrangement refluxes a portion of said retentate gasinto said permeate side.
 43. The system of claim 37, wherein said heatercomprises a heat exchanger for transferring heat from a waste heatsource to said liquid, and wherein said quantity of thermal energycomprises thermal energy from a source selected from the groupconsisting of (a) a waste heat, (b) solar heat, (c) low level heat, (d)a furnace, (e) flue gas, (f) geothermal heat, (g) steam, (h) hot water,(i) burning fuel, (j) burning gas, (k) electrical and (l) geothermal.44. The system of claim 37, further comprising a heat exchanger fortransferring energy between said vapor-containing gas and said liquid,before said liquid enters said gas-liquid contactor and after saidvapor-containing gas exits from said gas-liquid contactor.
 45. Thesystem of claim 37, further comprising a heat exchanger for transferringenergy between said process gas and said liquid, before said process gasenters said gas-liquid contactor and after said liquid exits from saidgas-liquid contactor.
 46. The system of claim 37, wherein saidgas-liquid contactor comprises a unit selected from the group consistingof (a) cooling tower, (b) a spray contactor, (c) an atomizing contactor,(d) a dripping contactor, (e) a sprinkler contactor, (f) a wet padcontactor, (g) a packed column, (h) a plates column, (i) a baffle tower,(j) a membrane contactor, (k) a humidifier, (l) an evaporator and (m) aflash evaporator. 47-50. (canceled)